The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
The technical field of the present disclosure is that of the needleless, pre-filled and disposable injection devices, operating with an energy source such as for example a gas generator, and used for the intradermal, subcutaneous and intramuscular injections of liquid active ingredient for therapeutic use in human or veterinary medicine.
The active ingredient is constituted by a more or less viscous liquid, a mixture of liquid, or a gel. The active ingredient may also be a solid dissolved in a solvent suitable for the injection or be constituted of a powdery solid suspended at a certain concentration in a suitable liquid. The particle size of the active ingredient must then be compatible with the diameter of the ducts to avoid sealing them.
An injection device includes, in a known manner, as for example in the patent application FR-A-2815544 (equivalent to WO 02/34317), a body successively comprising a gas generator, an expansion chamber, a reservoir containing the liquid active ingredient and an injection system.
The reservoir is constituted by a glass tube which is inserted into a tubular housing delimited by the body of the device, the tube being sealed by an upstream piston and a downstream piston between which the liquid active ingredient is contained.
The free downstream or lower end of the reservoir cooperates with an injection nozzle which delimits at least one injection channel extending axially along an injection axis.
The injection nozzle is delimited axially by an upper face axially bearing on the reservoir, and a lower injection face adapted to cooperate with a closure cap.
Furthermore, the injection device includes a hollow cover which wraps the body and which delimits a lower opening adapted for the passage of the injection nozzle.
In order to allow the injection of the active ingredient, the body is slidably mounted in the cover, from bottom to top along a sliding axis, between a rest position and an injection position, the driving of the body being carried out when the user presses the injection nozzle on his skin.
The displacement of the body in the cover allows the triggering of the gas generator, generating a pressurized gas which drives the pistons in displacement to inject the active ingredient through the skin of the patient, by passing through the injection nozzle.
There is known an injection device which is equipped with a generally T-shaped elastically deformable membrane, which comprises a radial annular disc which is interposed axially between the upper end of the reservoir and a seat formed by the body, and a tubular portion which extends axially in the reservoir, from the annular disc.
The tubular portion of the membrane is designed to extend axially under the effect of the pressurized gas, in order to drive the pistons in displacement.
The pressure of the gas also deforms the membrane radially, such that the membrane engages on the inner wall of the glass reservoir.
The friction between the membrane, which is generally made of elastomer, and the glass wall of the reservoir, is significant and absorbs a significant portion of the energy required for the elongation and extension of the tubular portion of the membrane in the reservoir.
In order to overcome this issue, it is known to lubricate the membrane in order to limit the friction between the membrane and the reservoir.
Although effective, the lubrication is a restrictive step during the production and assembly of the injection device.